The present invention relates generally to the art of completing subterranean wells having lateral bores extending from parent bores thereof and, in a preferred embodiment thereof, more particularly provides apparatus for reentering the parent bores after the lateral bores have been cased and associated methods.
It is well known in the art of drilling subterranean wells to form a parent bore into the earth and then to form one or more bores extending laterally therefrom. Generally, the parent bore is first cased and cemented, and then a tool known as a whipstock is positioned in the parent bore casing. The whipstock is specially configured to deflect milling bits and drill bits in a desired direction for forming a lateral bore. A mill, otherwise referred to as a cutting tool, is lowered into the parent bore suspended from drill pipe and is radially outwardly deflected by the whipstock to mill a window in the parent bore casing and cement. Directional drilling techniques may then be employed to direct further drilling of the lateral bore as desired.
The lateral bore is then cased by inserting a tubular liner from the parent bore, through the window previously cut in the parent bore casing and cement, and into the lateral bore. In a typical lateral bore casing operation, the liner extends somewhat upwardly into the parent bore casing and through the window when the casing operation is finished. In this way, an overlap is achieved wherein the lateral bore liner is received in the parent bore casing above the window. The lateral bore liner is then cemented in place by forcing cement between the liner and the lateral bore. The cement is typically also forced between the liner and the window, and between the liner and the parent bore casing where they overlap. The cement provides a seal between the liner, the parent bore casing, the window, and the lateral bore.
It will be readily appreciated that because the liner overlaps the parent bore casing above the window, extends radially outward through the window, and is cemented in place, that access to the parent bore below the liner is prevented at this point. In order to gain access to the parent bore below the liner, an opening must be provided through the liner. However, since the liner is extending radially outward and downward from the parent bore, cutting an opening into the sloping inner surface of the liner is a difficult proposition at best. Furthermore, it is desirable to obtain "full-bore access" to the parent wellbore below the liner so that the same-sized tools can be diverted into either the lateral wellbore, the parent wellbore below the liner, or any other equivalent-bore lateral wellbore extending from the parent wellbore.
Several apparatus and methods for cutting the opening through the liner to gain access to the lower portion of the parent bore have been devised. Each of these, however, have one or more disadvantages which make their use inconvenient or uneconomical. Some of these disadvantages include inaccurate positioning and orienting of the opening to be cut, complexity in setting and releasing portions of the apparatus, and danger of leaving portions of the apparatus in the well necessitating a subsequent fishing operation. Furthermore, none of the prior art teaches apparatus or a method of obtaining full-bore access to (1) the parent wellbore below the intersection of the parent and lateral wellbores and (2) all equivalent-bore lateral wellbores extending from the parent wellbore.
From the foregoing, it can be seen that it would be quite desirable to provide apparatus for gaining access to the lower portion of the parent wellbore which is convenient and economical to use, which provides accurate positioning and orienting of the opening to be cut, which is not complex to set and release, and which reduces the danger of leaving portions of the apparatus in the well. Furthermore, it is desirable to establish full-bore access to the parent wellbore below the intersection of the parent and the lateral wellbores. It is accordingly an object of the present invention to provide such apparatus and associated methods of completing a subterranean well.